Humoral immunity provides protection against pathogenic viral, bacterial, and parasitic infections and is mediated by antibodies that are produced following the differentiation of B cells into antibody secreting plasma cells (PCs). Depending on the type of antigen, T cell independent (TI) and dependent (TD) processes primarily shape the PC population into short-lived or long-lived PCs (SLPCs and LLPCs, respectively). The latter, along with memory B cells, provide life-long humoral immunity. Although the major transcription factor networks and gene expression differences between B cells and PCs have been described, the mechanisms by which these cells adopt a heritable cell fate program and how that program differs between TD and TI immune responses is unknown. From our preliminary data, we propose that these programs are orchestrated and maintained through epigenetic mechanisms that allow for heritable, defined terminal differentiation states and that these programs will be distinct between TD and TI processes. Identifying the programs and factors responsible for PC formation and maintenance is important for our ability to design more effective immune- based treatments for infectious disease and cancer, as well as to treat autoimmune diseases that have antibody as a pathogenic component. Herein, we will take advantage of the newly developed B cell tetramers to track influenza-specific B cells following infection of normal mice and those that lack CD4 T cells. Thus, using the same infection model, TI and TD responses can be compared. In Aim 1 we will test the hypothesis that DNA methylation changes are distinct between TI and TD responses and that the de novo DNA methyltransferases (DNMT3a/b) are required to extinguish the B cell program and lock in the LLPC program. In Aim 2, we will test the hypothesis that the histone code associated with enhancers and promoters is distinct between TI and TD responses. We will also test the hypothesis that enhancer and promoter decommissioning (silencing) is required to exit the B cell fate by examining the role of the lysine specific demethylase 1 (LSD1) during the above immune processes. Aim 3 will focus on the fact that multiple cell divisions are required for nave B cells to differentiate into plasma cells. From our data, we hypothesize that it is during these divisions that a step-wise reorganization of the epigenome occurs, such that the B cell program is silenced and the plasma cell program is imprinted. We will test this in vivo by isolating wild-type and DNMT3a/b- and LSD1 deficient cells, representing specific cell divisions, during TI and TD dependent responses to influenza and assessing DNA methylation and chromatin accessibility changes that occur. Together the data and analyzes derived from these studies will define the transcriptional and epigenetic programs, metabolic pathways, and networks used by plasma cells, which ultimately could be used to design novel treatment regiments to improve the ability to form LLPC or to inhibit such processes in autoimmunity. The information gained in this project will integrate completely with each of the other projects as they seek to identify plasma cell epigenetic programs.